2017 ASHS Annual Conference

Recent work in our lab has shown that invasive algae species can serve as a source of potassium (K) for crops, but questions remain regarding differences in pattern and mechanisms of release of K from these materials. Our objective here was to study the patterns of K release from the dry biomass of 3 invasive red algae (Eucheuma denticulatum, Gracilaria salicornia, and Kappaphycus alvarezii) as compared with synthetic potassium fertilizers (potassium chloride (KCl) and potassium nitrate (KNO₃). Three leachate column studies were undertaken in the laboratory with 3 media types: peat moss, Oxisol, and Mollisol soils. Two rates of K (112 and 336 kg·ha^-1) were provided, adjusting for K concentration of the materials. Treatments were replicated 3 times. Columns were leached weekly with DI water over a period of 16 weeks. The collected leachates were analyzed for K concentration using a K ion selective electrode, with NaClO₄ as an ion strength adjustment buffer. Results showed the concentrations of K were much higher in the leachates treated with synthetic K in the first 6^th week (4100-4200 ppm) and sharply declined at later weeks. In contrast, the release of K from algae treated leachates was slower in the first 3 weeks and reached highest at 8-9 weeks (2800-3400 ppm). Interestingly, the release rate of K from G. salicornia was consistently and significantly lower than measured for E. denticulatum or K. alvarezii in all media. To better understand the slow release of K from G.salicornia, a leachate study was conducted with oxisol soils and dried gels of agar extracted from G. salicornia and carrageenan from K. alvarezii at two rates. A total of 12 leachate samples collected over 6 weeks, measured for K. Cumulative recovery of K from agar was significantly lower (10-12%) than carrageenan . We conclude that the rate and total amount of K released from algae was lower than synthetic K fertilizers applied at equivalent rates of K, and that differences in release among algal species may be explained in part by differences in cell wall composition.